(Reuters) -Shares of U.S. biotech companies fell as much as 10% premarket on Monday following reports that a top vaccine official at the U.S. Food and Drug Administration had resigned, fanning worries over slower reviews for breakthrough treatments.

Peter Marks, who played a key role in U.S. President Donald Trump's first term in developing COVID-19 vaccines, will leave effective April 5, the Wall Street Journal and other media outlets reported on Friday.

As director of the FDA's Center for Biologics Evaluation and Research, Marks has publicly supported programs that expedited the development of rare disease treatments and gene therapies during his tenure.

Shares of gene therapy makers including Taysha Gene Therapies ( TSHA ), Solid Biosciences ( SLDB ) and Sarepta Therapeutics ( SRPT ) were down between 4% and 10% in premarket trading.

The resignation "could put some pressure on companies whose drugs are currently, or planned to be, under review by (the FDA)," said Truist Research analyst Joon Lee in a research note.

The three companies are all developing gene therapies to treat rare conditions. Shares of vaccine maker Moderna ( MRNA ) also fell 2.7% to $30.28 before the opening bell.

The reports said Marks was given the choice by a Health and Human Services (HHS) official to resign or be fired.

Marks did not respond to a request for comment over email on Monday.

Last week, U.S. Secretary of Health and Human Services Robert F. Kennedy Jr. announced plans to reshape federal public health agencies. The overhaul will involve cutting 10,000 jobs, including 3,500 at the FDA.

(Reporting by Manas Mishra in Bengaluru; Editing by Sriraj Kalluvila)